High pressure gas spring controls for improved vehicle leveling

ABSTRACT

A suspension system includes a spring assembly including a gas spring and an accumulator, and a controller. The accumulator is coupled to the gas spring and includes a bladder. The accumulator has a compressed state and an uncompressed state. The controller is configured to a) determine a target amount of gas in the spring assembly and b) adjust the amount of gas in the spring assembly towards the target amount of gas based on a pressure difference across the bladder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/957,319, filed Apr. 19, 2018, which claims the benefit of U.S.Provisional Application No. 62/492,041, filed Apr. 28, 2017, and U.S.Provisional Application No. 62/491,724, filed Apr. 28, 2017, all ofwhich are incorporated herein by reference in their entireties.

BACKGROUND

The present application relates to suspension systems for vehicles. Morespecifically, the present application relates to controlling a gasspring in a vehicle suspension system.

Many modern vehicles include suspension systems. These suspensionsystems typically include a spring and a damper (or other componentsthat emulate or otherwise mimic the features of a spring and a damper).In combination, the spring and damper regulate a ride height for thevehicle.

SUMMARY

According to one embodiment, a suspension system includes a springassembly including a gas spring and an accumulator, and a controller.The accumulator is coupled to the gas spring and includes a bladder. Theaccumulator has a compressed state and an uncompressed state. Thecontroller is configured to a) determine a target amount of gas in thespring assembly and b) adjust the amount of gas in the spring assemblytowards the target amount of gas based on a pressure difference acrossthe bladder.

According to another embodiment, a vehicle includes a suspension systemand a controller. The suspension system includes a spring assemblyincluding a gas spring and an accumulator. The accumulator is coupled tothe gas spring and includes a bladder. The accumulator has a compressedstate and an uncompressed state. The controller is configured to a)determine a target amount of gas in the spring assembly and b) adjustthe amount of gas in the spring assembly towards the target amount ofgas based on the pressure difference across the bladder.

According to another embodiment, a method of controlling a gas spring ina suspension system includes detecting at least one of a) a firstpressure on a first side of a bladder of an accumulator coupled to thegas spring and b) a second pressure on a second side of the bladderopposite the first side. The method includes determining a target amountof gas in a spring assembly that includes the accumulator and the gasspring. The method includes adjusting the amount of gas in the springassembly towards the target amount of gas based on a difference betweenthe first pressure and the second pressure.

The invention is capable of other embodiments and of being carried outin various ways. Alternative exemplary embodiments relate to otherfeatures and combinations of features as may be recited herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a side view of a vehicle, according to an exemplaryembodiment;

FIG. 2 is a perspective view of an axle assembly, according to anexemplary embodiment;

FIG. 3 is a perspective view of a suspension system, according to anexemplary embodiment;

FIG. 4 is a perspective view of a gas spring in a first configuration,according to an exemplary embodiment;

FIG. 5 is a side view of the gas spring of FIG. 4 in a secondconfiguration, according to an exemplary embodiment;

FIG. 6 is a side view of a gas spring assembly, according to anexemplary embodiment;

FIG. 7 is a front view of the gas spring assembly of FIG. 5, accordingto an exemplary embodiment;

FIG. 8A is a sectional view of the gas spring assembly of FIG. 7, takenalong line 8A-8A of FIG. 7, according to an exemplary embodiment;

FIG. 8B is a schematic view of a gas spring assembly, according to anexemplary embodiment;

FIG. 9 is a detailed diagram of a vehicle suspension control system,according to an exemplary embodiment;

FIG. 10 is a force diagram of a vehicle, according to an exemplaryembodiment; and

FIGS. 11A and 11B are detailed diagrams of a gas spring assembly,according to an exemplary embodiment.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the presentapplication is not limited to the details or methodology set forth inthe description or illustrated in the figures. It should also beunderstood that the terminology is for the purpose of description onlyand should not be regarded as limiting.

According to an exemplary embodiment, a vehicle includes variouscomponents that improve performance relative to traditional systems. Thevehicle may be configured for operation on both paved and rough,off-road terrain. As such, the suspension system may be correspondinglyconfigured to support the weight of the vehicle while providing acomfortable ride quality on both paved and rough, off-road terrain. Insome embodiments, the suspension system is configured to change the rideheight of the vehicle by lifting or lowering the body of the vehiclewith respect to the ground.

According to the exemplary embodiment shown in FIG. 1, a vehicle, shownas vehicle 10, includes a chassis, shown as frame 12, that supports abody or body assembly including a first portion, shown as front cabin20, and a second portion, shown as mission equipment 30. As shown inFIG. 1, the mission equipment 30 is disposed behind the front cabin 20.The frame 12 of the vehicle 10 engages a plurality of tractiveassemblies, shown as front tractive assemblies 40 and rear tractiveassemblies 42. According to an exemplary embodiment, the vehicle 10 is amilitary ground vehicle. In other embodiments, the vehicle 10 is anoff-road vehicle such as a utility task vehicle, a recreationaloff-highway vehicle, an all-terrain vehicle, a sport utility vehicle,and/or still another vehicle. In yet other embodiments, the vehicle 10is another type of off-road vehicle such as mining, construction, and/orfarming equipment. In still other embodiments, the vehicle 10 is anaerial truck, a rescue truck, an aircraft rescue and firefighting (ARFF)truck, a concrete mixer truck, a refuse truck, a commercial truck, atanker, an ambulance, a personal vehicle (e.g., an automobile, amotorcycle, etc.), and/or still another vehicle.

According to an exemplary embodiment, the frame 12 defines alongitudinal axis. The longitudinal axis may be generally aligned with aframe rail of the frame 12 of the vehicle 10 (e.g., front-to-back,etc.). In some embodiments, the vehicle 10 includes a plurality of fronttractive assemblies 40 and/or a plurality of rear tractive assemblies 42(e.g., one, two, etc.). The front tractive assemblies 40 and/or the reartractive assemblies 42 may include brakes (e.g., disc brakes, drumbrakes, air brakes, etc.), gear reductions, steering components, wheelhubs, wheels, tires, and/or other features. As shown in FIG. 1, thefront tractive assemblies 40 and the rear tractive assemblies 42 eachinclude tractive elements, shown as wheel and tire assemblies 44. Inother embodiments, at least one of the front tractive assemblies 40 andthe rear tractive assemblies 42 include a different type of tractiveelement (e.g., a track, etc.).

According to an exemplary embodiment, the front cabin 20 includes one ormore doors, shown as doors 22, that facilitate entering and exiting aninterior of the front cabin 20. The interior of the front cabin 20 mayinclude a plurality of seats (e.g., two, three, four, five, etc.),vehicle controls, driving components (e.g., steering wheel, acceleratorpedal, brake pedal, etc.), etc. According to the exemplary embodimentshown in FIG. 1, the mission equipment 30 includes a cargo bodyconfigured to facilitate transporting various military equipment (e.g.,medical supplies, ammunition, weapons, missiles, personnel, etc.). Inother embodiments, the mission equipment 30 includes a truck bed or aflat bed. In some embodiments, the mission equipment 30 additionally oralternatively includes a boom lift. In another embodiment, the missionequipment 30 includes an at least partially enclosed troop transportcabin configured to facilitate transporting troops (e.g., eight, ten,twelve, twenty, etc.) with the vehicle 10.

According to an exemplary embodiment, the vehicle 10 includes apowertrain system. The powertrain system may include a primary driver(e.g., an engine, a motor, etc.), an energy generation device (e.g., agenerator, etc.), and/or an energy storage device (e.g., a battery,capacitors, ultra-capacitors, etc.) electrically coupled to the energygeneration device. The primary driver may receive fuel (e.g., gasoline,diesel, etc.) from a fuel tank and combust the fuel to generatemechanical energy. A transmission may receive the mechanical energy andprovide an output to the generator. The generator may be configured toconvert mechanical energy into electrical energy that may be stored bythe energy storage device. The energy storage device may provideelectrical energy to a motive driver to drive at least one of the fronttractive assemblies 40 and the rear tractive assemblies 42. In someembodiments, each of the front tractive assemblies 40 and/or the reartractive assemblies 42 include an individual motive driver (e.g., amotor that is electrically coupled to the energy storage device, etc.)configured to facilitate independently driving each of the wheel andtire assemblies 44. In some embodiments, a transmission of the vehicle10 is rotationally coupled to the primary driver, a transfer caseassembly, and one or more drive shafts. The one or more drive shafts maybe received by one or more differentials configured to convey therotational energy of the drive shaft to a final drive (e.g., half-shaftscoupled to the wheel and tire assemblies 44, etc.). The final drive maythen propel or move the vehicle 10. In such embodiments, the vehicle 10may not include the generator and/or the energy storage device. Thepowertrain of the vehicle 10 may thereby be a hybrid powertrain or anon-hybrid powertrain. According to an exemplary embodiment, the primarydriver is a compression-ignition internal combustion engine thatutilizes diesel fuel. In alternative embodiments, the primary driver isanother type of device (e.g., spark-ignition engine, fuel cell, electricmotor, etc.) that is otherwise powered (e.g., with gasoline, compressednatural gas, hydrogen, electricity, etc.).

Referring to FIG. 2, an axle assembly 210 is configured for use with thevehicle 10. The axle assembly 210 may be incorporated into the fronttractive assembly 40 and/or the rear tractive assemblies 42. Accordingto an exemplary embodiment, the axle assembly 210 includes adifferential 212 connected to half shafts 214, which are each connectedto a wheel end assembly 216. The wheel end assembly 216 is at leastpartially controlled (e.g., supported) by a suspension system 218, whichincludes a spring 220, a damper 222, an upper support arm 224, and alower support arm 226 coupling the wheel end assembly 216 to the vehiclebody or part thereof (e.g., chassis, side plate, hull).

According to an exemplary embodiment, the differential 212 is configuredto be connected with a drive shaft of the vehicle 10, receivingrotational energy from the primary driver of the vehicle 10, such as adiesel engine. The differential 212 allocates torque provided by theprimary driver between half shafts 214 of the axle assembly 210. Thehalf shafts 214 deliver the rotational energy to the wheel-endassemblies 216 of the axle assembly 210. The wheel end assemblies 216may include brakes, gear reductions, steering components, wheel hubs,wheels, and other features. As the vehicle 10 travels over uneventerrain, the upper and lower support arms 224, 226 at least partiallyguide the movement of each wheel end assembly 216, and a stopper 228provides an upper bound to movement of the wheel end assembly 216.

Referring to FIG. 3, according to an exemplary embodiment, thesuspension system 218 includes one or more high-pressure gas components,where the spring 220 is a high-pressure gas spring 220. In someembodiments, the suspension system 218 further includes at least onehigh-pressure gas pump 230. In some such embodiments, the suspensionsystem 218 includes separate high-pressure gas pumps 230 associated witheach spring 220 and damper 222 set. In preferred embodiments, the gas ofthe pump 230 and spring 220 includes (e.g., is at least 90%, at least95%) an inert gas such as nitrogen, argon, helium, etc., which may bestored, provided, or received in one or more reservoirs (e.g., centralreservoir, tank).

During operation, the pump 230 selectively provides gas, under pressure,to the high-pressure gas spring 220 and/or to reservoirs, tanks,accumulators, or other devices. In some contemplated embodiments, two ormore dampers 222 of the vehicle are cross-plumbed with lines 232 (e.g.,hydraulic lines). Lines 232 may connect dampers 222 on opposite sides ofthe axle assembly 210 in a “walking beam” configuration.

Referring to FIG. 4 and FIG. 5, a gas spring 310 includes a cylinder 312coupled to a rod 314. The cylinder 312 has a cap end 316, a rod end 318,and a side wall 320 (e.g., cylindrical side wall) extending between thecap and rod ends 316, 318. A chamber is formed between the cylinder 312and the rod 314. The chamber may be a space defined by the interior ofthe cylinder 312 surrounded by side wall 320 and between cap end 316 androd end 318. Nitrogen or another gas held in the chamber compresses orexpands in response to relative movement between the rod 314 and thecylinder 312 to provide the receipt, storage, or release of potentialenergy by the gas spring 310.

The rod 314 is configured to translate with respect to the cylinder 312.According to an exemplary embodiment, the rod 314 is coupled to orincludes a piston that forms a wall of the chamber. When the rod 314translates relative to the cylinder 312, the piston changes the volumeof the chamber, compressing the gas in the chamber or facilitatingexpansion of the gas. The gas in the chamber resists compression,providing a force that is a function of the compressibility of the gas,the area of the piston, the volume and geometry of the chamber, and theinitial state (e.g., initial pressure) of the gas, among other factors.The gas spring 310 receives potential energy, stored in the gas, as thegas is compressed and releases the potential energy as the gas expands.

The cylinder 312 of the gas spring 310 is preferably cylindrical due tostructural benefits associated with cylindrical pressure vessels.However, in other contemplated embodiments, the cylinder 312 may besubstituted for a body having another geometry. In some contemplatedembodiments, the chamber is formed in, or at least partially formed in,the rod 314. In one such embodiment, the chamber spans both the cylinder312 and at least a portion of the interior of the rod 314.

In some embodiments, the gas spring 310 includes at least one port 322(e.g., aperture, inlet) that may be opened to facilitate providing gas(e.g., inert gas) to or from the chamber. The chamber of the gas spring310 is substantially sealed when the port 322 is not open. In someembodiments, the port 322 is coupled to an accumulator or to one or morereservoirs. In some embodiments, the spring 310 includes separate portsassociated with the accumulator and the pump.

In some embodiments, the gas spring 310 further includes at least oneport 324 that may be opened to facilitate coupling a pressurizedreservoir of a higher or a lower pressure the gas spring 310. Couplingthe higher pressure reservoir to the gas spring 310 increases thepressure in the gas spring 310, causing the gas spring 310 to expand andincreasing the ride height of the axle assembly. Conversely, couplingthe lower pressure reservoir to the gas spring 310 decreases thepressure in the gas spring 310, causing the gas spring 310 to contractand decreasing the ride height of the axle assembly. In someembodiments, the spring 310 includes separate ports 324 for providinghydraulic fluid to the internal volume and for receiving hydraulic fluidfrom the internal volume.

In other contemplated embodiments, the gas spring 310 is coupleddirectly to a pump to increase or decrease pressure in the gas spring310 to provide a desired ride height. In still another contemplatedembodiment, a gas spring further includes at least one port that may beopened to facilitate providing hydraulic fluid (e.g., oil) to or from aninternal volume of the gas spring. The internal volume for hydraulicfluid is separated from the chamber for gas. In such contemplatedembodiments, adding or removing of hydraulic fluid from the internalvolume changes the overall length of the gas spring for different rideheights of the suspension system. However using pressurized gas tochange the length of the gas spring 310 may be preferable in someembodiments because of reduced losses (e.g., friction, drag) associatedwith a flow of gas (e.g., nitrogen) compared to losses associated withthe flow of hydraulic fluid (e.g., oil).

Referring now to FIG. 6 through FIG. 8B, a gas spring assembly 410includes a cylinder 412 coupled to a rod 414, and an accumulator 416. Afirst chamber 418 is formed between the cylinder 412 and the rod 414 anda second chamber 420 is formed in the accumulator 416. According to anexemplary embodiment, the accumulator 416 includes a rigid exterior 424(e.g., shell, housing) and a flexible, inflatable bladder 426 within therigid exterior 424. The second chamber 420 is located between the rigidexterior 424 and the bladder 426. According to an exemplary embodiment,the accumulator 416 is positioned proximate to the cylinder 412 and rod414, and the second chamber 420 of the accumulator 416 is connected tothe first chamber 418, formed between the cylinder 412 and rod 414, byway of a gas transfer conduit 422. The gas transfer conduit 422 mayinclude a valve 428 (e.g., check valve, poppet) positioned to controlaccess between the first and second chambers 418, 420. The valve 428 mayoptionally disconnect the accumulator 416 from the first chamber 418and/or contain gas in the second chamber 420 having a pressure exceedingor lower than gas in the first chamber 418.

In some embodiments, when the valve 428 is open, the first chamber 418is in gaseous communication with the second chamber 420 such that acontinuous body of gas extends between the two chambers 418, 420. Nointermediate hydraulic fluid or mechanical element is included totransfer energy from the first chamber 418 to the second chamber 420 orvice versa. In some such embodiments, the only hydraulic fluidassociated with the gas spring assembly 410 is a thin film between therod and cylinder that moves during compression or extension of the rod414. The continuous body of gas for gaseous communication between thefirst and second chambers 418, 420 is intended to reduce frictionallosses associated with energy transfer between the first and secondchambers 418, 420, as may otherwise occur with hydraulic or mechanicalintermediate elements. However, in other contemplated embodiments,hydraulic or mechanical intermediate elements may be included.

Referring specifically to FIG. 8A and FIG. 8B, in some embodiments, thecylinder 412 is double acting cylinder such that a third chamber 440located on the opposite side of the rod 414 may additionally bepressurized or depressurized. A gas transfer conduit 422 facilitatesproviding gas (e.g., inert gas) to or from the third chamber 440. Insuch embodiments, pressurizing the third chamber 440 actively retractsthe rod 414 (e.g., as opposed to using gravity to retract the rod 414,etc.). The rod may be retracted more rapidly using a double actingcylinder than with a single acting cylinder. By way of another example,the rod 414 may be locked in a single location, whereas it may otherwiseextend (e.g., if the wheel connected to it was not supported, etc.). Byway of another example, the additional force on the rod 414 from thethird chamber 440 may be used to overcome friction that might otherwiseprevent retraction of the rod 414 (e.g., stiction forces or tire scrub).

During use of the gas spring assembly 410, in some embodiments, thebladder 426 is inflated to an initial pressure. As the rod 414 andcylinder 412 are moved together, such as when the associated vehicledrives over a bump, gas in the chamber 418 compresses, providing a firstspring rate for the gas spring assembly 410. In such embodiments, thepressure of the gas in the first chamber 418 is communicated to theaccumulator 416 through the transfer conduit 422. If the pressure of thegas communicated from the first chamber 418 is below the initialpressure of the bladder 426, the gas spring assembly 410 will respond tothe bump with the first spring rate. However, if the pressure of the gascommunicated from the first chamber 418 exceeds the initial pressure inthe bladder 426, then the bladder 426 will compress, increasing theeffective volume of the second chamber 418, which provides a secondspring rate to the gas spring assembly 410. The bladder 426 therebyprovides a softening of the suspension against heavy vertical loads.

In some such embodiments, a pump is coupled to the bladder 426 toincrease the initial pressure of the bladder 426 and thereby increasethe threshold amount of loading required to achieve compression of thebladder 426, which would increase the loading required to initiate thesecond spring rate. Alternatively, gas may be released from the bladder426 to decrease the threshold. As such, the value of the initialpressure of the bladder 426 may be set to achieve a desiredresponsiveness of the gas spring assembly 410. The first and secondspring rates reduce peak forces on the vehicle, improving the ridequality and durability of the vehicle. Tuning of the thresholdfacilitates adjustment of the response of the gas spring assembly 410depending upon a particular vehicle application.

According to an exemplary embodiment, the gas spring assembly furtherincludes a sensor 442 integrated with the gas spring assembly 410 andconfigured to sense the relative configuration of the rod 414 andcylinder 412. In some embodiments, the sensor 442 provides a signal(e.g., digital output) that is indicative of the ride height of theassociated suspension system based upon the relative configuration ofthe rod 414 and cylinder 412. In contemplated embodiments, the sensor442 includes a linear variable differential transformer (LVDT), where ashaft of the LVDT extends through the cylinder 412 to the rod 414. Asthe rod 414 and cylinder 412 move relative to one another, the shaft ofthe LVDT provides a signal (e.g., inductive current) that is a functionof the movement of the shaft.

Referring now to FIG. 9, a detailed diagram of a vehicle suspensioncontrol system is shown, according to an exemplary embodiment. Vehicle800 is shown to include gas spring assemblies 410, 802, 804, and 806.Although the vehicle suspension control system is shown to control fourgas spring assemblies (e.g., two gas spring assemblies coupled to afront tractive assembly 40 and two gas spring assemblies coupled to arear tractive assembly 42), it should be understood that the vehicle 10may include any number of gas spring assemblies (e.g., four, six, eight,etc.) and that the vehicle suspension control system may provideassociated control. Suspension controller 820 communicates with springassemblies 410, 802, 804 and 806 with data lines 830, 832, 834, and 836,respectively. Suspension controller 820 also communicates withcontroller 822 with data line 838. Suspension controller 820 includesprocessor 824 and memory 826. Data lines 830, 832, 834, 836, and 838 maybe any type of communications medium capable of conveying electronicdata between suspension controller 820 and spring assemblies 410, 802,804, 806, and controller 822. Data lines 830, 832, 834, 836, 838 may bewired connections, wireless connections, or a combination of wired andwireless connections. In some embodiments, data lines 830, 832, 834,836, 838 are redundant connections. For example, data line 830 mayinclude two or more independent connections between suspensioncontroller 820 and spring assembly 410. In another example, data line830 may include individual connections between suspension controller 820and the sensors and controls of spring assembly 410 (e.g., springpressure sensor 840, valve controls 848, etc.).

Spring assemblies 410, 802, 804, 806 each include sensor and controlequipment coupled to data lines 830, 832, 834, and 836. For example,spring assembly 410 may have a spring pressure sensor 840, accumulatorpressure sensor 842, temperature sensor 844, pump controls 846, valvecontrols 848, and spring length sensor 850. Pump controls 846 controlthe operation of one or more pumps and/or high- and/or low-pressuresources that provide pressurized gas to or from a gas spring and/or anaccumulator in spring assembly 410. Valve controls 848 control one ormore valves that regulate gas flow between the one or more pumps, thegas spring, and the accumulator. Spring pressure sensor 840 measures thepressure in the gas spring of spring assembly 410 and provides themeasured data to suspension controller 820 with data line 830.Accumulator pressure sensor 842 measures the pressure in the accumulatorof spring assembly 410 and provides the measured data to suspensioncontroller 820 with data line 830. Spring assembly 410 may also includetemperature sensor 844 within the accumulator of spring assembly 410.Spring length sensor 850 measures the current length of the gas springin spring assembly 410. In other embodiments, spring assemblies 410,802, 804, 806 include any number of sensors and controls. For example,accumulator pressure sensor 842 may include two or more pressure sensorsto provide redundancy for the suspension system in vehicle 800.

Suspension controller 820 is also shown to communicate with controller822 with data line 838. Controller 822 may be one or moremicroprocessors that control non-suspension functions of vehicle 800.For example, controller 822 may control the timing of the engine invehicle 800, the electrical power sent to various lights in vehicle 800,etc. or control any other non-suspension related electronic functions ofvehicle 800. In some embodiments, controller 822 is separate fromsuspension controller 820 and communicates with suspension controller820 with data line 838. In other embodiments, suspension controller 820is a part of (or the same as) controller 822.

Controller 822 may also include circuitry that provides an interface fora user. For example, controller 822 may communicate with a handheldcomputing device operated by a user, and the controller 822 may displayinformation to and/or receive input from the user via the handheldcomputing device. In other embodiments, controller 822 may communicatewith a user interface that includes one or more interactive devices(e.g., a touch-screen display, a keyboard, a mouse, voice-activatedcontrols, etc.) and non-interactive devices (e.g., a monitor, a speaker,etc.) located within vehicle 800. Controller 822 provides the userinteractive data to suspension controller 820 with data line 838 andreceives data from suspension controller 820 to be presented to a user.For example, a user may provide a preferred vehicle height to suspensioncontroller 820 with controller 822 and/or view the current pressure fora given spring using data provided by suspension controller 820 to auser display via controller 822.

Referring now to FIG. 9, a force diagram of the vehicle suspensionsystem of vehicle 800 is shown, according to an exemplary embodiment.The wheels of vehicle 800 experience resistance forces FFL 906, FFR 908,FRL 910, and FRR 912 from the ground, which correspond to the frontleft, front right, rear left, and rear right tires, respectively.Vehicle 800 also has a center of mass (e.g., center of gravity) 902which provides downward force FCG 904.

The suspension controller 820 may control the suspension system ofvehicle 800 by calculating a target quantity of gas for each spring andcontrolling the valves and/or pumps in each spring assembly to achievethe target quantity. Suspension controller 820 may calculate the targetquantity of gas using a mass estimate for vehicle 800 and a spring gasvolume target at a target ride height. Ride height may correspond with alevel or mostly level position for vehicle 800. For example, each springassembly of vehicle 800 may provide equal spring lengths when vehicle800 is at rest on a flat surface. In real world operation, adjustment ofthe suspension of vehicle 800 may not provide an entirely level positiondue to various environmental conditions (e.g., uneven terrain, friction,etc.). However, the effects of these environmental conditions may bemitigated using the gas law: PV=nRT where P is the spring pressure, V isthe spring volume, n is the amount of gas, R is the universal gasconstant approximately equal to 8.314 J/(K*mol), and T is the measuredtemperature in Kelvin. The suspension controller 820 may assume that thetemperature of the gas inside each spring assembly does not changeappreciably while adjusting the suspension system such that the amountof gas n is proportional to PV. Hereinafter, the amount of gas will bereferred to as Q, where Q=PV and incorporates the constants T and R. Inother embodiments, the suspension controller 820 may account for thetemperature change such that Q=PV/T. The suspension controller 820 mayestimate value of Q using data from pressure sensors, temperaturesensors, volume sensors, or any other sensor in the suspension system ofvehicle 800. In one embodiment, Q is calculated using data from flowrate sensors without using data from pressure sensors. In otherembodiments, Q is estimated using data from pressure sensors. Thetemperature T may be measured (e.g., using sensor 844) prior toadjustment of the suspension. The temperature sensor 844 may be locatedinside the accumulator 416 or in the chamber 418. The suspensioncontroller 820 may be configured to assume the temperature is the sameon both sides of the bladder 426. In other embodiments, temperaturesensors 844 may be located inside the accumulator 416 and inside thechamber 418.

Suspension controller 820 may be configured to control the suspensionsystem of vehicle 800 by minimizing an error estimation calculated aserror=Q_(target)−Q_(current), where Q_(target) and Q_(current) are thetarget and current amounts of gas in the spring assembly 410,respectively. Suspension controller 820 may be configured to treat eachspring assembly as a set of smaller volumes, such that Q_(target) andQ_(current) can be calculated from the sum of the amounts of gas in eachindividual volume. Although the term “minimizing” is used with respectto the error calculation throughout the present specification, it is tobe understood that the error calculation is exemplary only and thatsuspension controller 820 may perform any number of calculations toreduce the difference between the Q_(target) value and the Q_(current)value. In other embodiments, suspension controller 820 may be configuredto employ other control methods such as adaptive control, robustcontrol, control methods that do not require the calculation of theactual mass, or any other control method.

Referring now to FIGS. 11A and 11B, detailed diagrams of spring assembly410 are shown, according to an exemplary embodiment. Spring assembly 410is shown with accumulator 416 not compressed (FIG. 11A) and compressed(FIG. 11B).

Suspension controller 820 is configured to calculate overall gas volumesof each spring assembly, V_(current) and V_(target). V_(current)corresponds to the current conditions of the vehicle 800 and may becalculated using the internal geometry of the spring assembly 410 andinformation from the various sensors. V_(target) corresponds to the“ideal” conditions for vehicle 800 and is calculated using the internalgeometry of the spring assembly 410 under these conditions. In anotherexample, the target volume may be calculated using the geometry ofspring chamber 418, the geometry of accumulator 416, and/or the geometryof flexible bladder 426 at the target ride height. In some embodiments,V_(target) is a fixed value and stored in the memory of suspensioncontroller 820. In other embodiments, V_(target) may be one or morevalues that account for different desired heights or non-idealconditions.

The suspension controller 820 is configured to calculate volumesV_(current) and V_(target) using the internal geometry of the springassembly. The volumes V_(current) and V_(target) have three smallervolumes: the volume of the accumulator V_(accumulator), a dead volumeV_(deadVol), and the volume inside the chamber 418 V_(strut). In thecalculation performed by the suspension controller 820, the accumulatorvolume V_(accumulator) corresponds to the fully inflated volume of theaccumulator 416 and is constant, regardless of the position of thebladder 426. The dead volume V_(deadVol) corresponds to a volume of gaspresent even at a minimum (i.e., fully compressed) spring length. Thedead volume V_(deadVol) includes the gas volume present in the chamber418 when spring is fully compressed and the volume of gas in varioustubes that connect the chamber 418 to other related components such asvalves, etc. The suspension controller 820 may be configured to treatthe dead volume V_(deadVol) as a constant. The volume V_(strut) varieswith spring length. In one embodiment, the suspension controller 820calculates V_(strut) by multiplying the cross-sectional area of thechamber 418 by the spring length as measured by the spring length sensor850. In another embodiment, corresponding values for spring length andV_(strut) are stored in a lookup table in the memory 826 of suspensioncontroller 820. The suspension controller 820 may be configured toreference the lookup table in addition to the spring length as measuredby the spring length sensor 850 to determine V_(strut).

Each volume (V_(accumulator), V_(deadVol), and V_(strut)) has anassociated pressure (P_(accumulator), P_(deadVol), and P_(strut),respectively). The suspension controller 820 may be configured to assumethat any flow restrictions between the dead volume and the springchamber 418 are negligible such that the pressure in the spring chamber418, P_(strut), and the pressure in the dead volume, P_(deadVol), areequal. The pressures in the accumulator 416 and the spring chamber 418may differ from one another, however, due to the separation between thetwo volumes imposed by the bladder 426. For the purposes of thecalculations herein, the pressure in the volume V_(accumulator) may betaken as the greater of the strut pressure P_(strut) and a chargepressure of the accumulator 416 P_(charge). The charge pressure may bethe uncompressed pressure of the accumulator 416 and may be set byadding or removing gas on the side of the bladder 426 opposite chamber418. In some embodiments, the charge pressure is set by a user prior tooperation of the vehicle 800. In other embodiments, the charge pressureis variable throughout operation of the vehicle (e.g., by control of apump coupled to the accumulator 416). In FIG. 11A, accumulator 416 hasnot been compressed. The pressure in accumulator 416 is greater than thepressure in spring chamber 418 (e.g., P_(accumulator)>P_(strut)), andthe accumulator pressure is the charge pressure (e.g.,P_(accumulator)=P_(charge)). In FIG. 11B, accumulator 416 is shown to becompressed. The pressure in the accumulator 416 is equal to the pressurein the spring chamber 418 (e.g., P_(accumulator)=P_(strut)). Regardlessof the position of the bladder 426, the pressure in the volumeV_(accumulator) will be uniform throughout. By way of example, ifbladder 426 is fully expanded, the pressure in the accumulator 416 isgreater than the pressure in the spring chamber 418, and the pressurethroughout volume V_(accumulator) is pressure P_(charge). By way ofanother example, if the bladder 426 is compressed, the pressure on bothsides of the bladder 426 is the same.

The suspension controller 820 is configured to calculate the amounts ofgas Q_(target) and Q_(current) from the sum of the amounts of gas ineach individual volume. The amount of gas in each individual volume befound by multiplying each individual volume (V_(accumulator),V_(deadVol), and V_(strut)) by its corresponding pressure(P_(accumulator), P_(deadVol), and P_(strut), respectively). Utilizingthe pressure relationships stated above, the controller is configured tocalculateQ_(current)=P_(strut,current)(V_(strut,current)+V_(deadVol))+max(P_(charge),P_(strut,current))V_(accumulator) andQ_(target)=P_(strut,target)(V_(strut,target)+V_(deadVol))+max(P_(charge),P_(strut,target))V_(accumulator), where max(A,B) returns the greater ofA and B. The suspension controller 820 is configured to measure thecurrent pressure P_(strut,current) using the spring pressure sensor 840.The suspension controller 820 calculates the current volumeV_(strut,current) using the spring length value measured by the springlength sensor 850. The dead volume V_(deadVol) and accumulator volumeV_(accumulator) may be constants stored in memory 826.

The suspension controller 820 incorporates the max(A,B) term to accountfor the potential difference in pressure between the strut volume andthe accumulator volume. Because of the bladder 426, the accumulatorvolume may be the greater of the two pressures P_(charge) and P_(strut).The incorporation of the max(A,B) term facilitates adjusting the heightof the vehicle 800 regardless of whether the accumulator 416 iscompressed. Other controllers without this term do not account for thegas in the accumulator 416, instead assuming the entire volume of thespring assembly has a consistent pressure. These controllers may not beable to adjust the height of the vehicle accurately when the accumulator416 is partially compressed. The value of pressure P_(charge) may beprovided by a user or measured by the accumulator pressure sensor 842when the accumulator 416 is not compressed. If the pressure P_(charge)is provided by a user, the vehicle 800 may not include the accumulatorpressure sensor 842.

The suspension controller 820 may be configured to determine the volumeV_(strut,target) using the desired suspension height. Each suspensionheight corresponds to a spring length depending on the geometry of thesuspension system. The spring length may be used to calculate the strutvolume as described above. The suspension controller 820 may determinethe desired suspension height from a variety of factors including, butnot limited to, a user input, the location of the center of gravity ofthe vehicle 800, and the desired ride height of the vehicle.

The pressure in the strut, P_(strut), forces the rod 314 out of thechamber and is proportional to the force delivered by the springassembly. Suspension controller 820 may calculate a target strutpressure, P_(strut,target), for each spring assembly using a massestimation for vehicle 800. Suspension controller 820 may simplify thecalculation of the mass estimation. For example, a linear relationshipmay be assumed between spring pressures and tire contact forces. Certaingeometric relationships in vehicle 800 may additionally or alternativelybe assumed to be uniform (e.g., front and rear track widths areidentical, each suspension corner is identical in dimensions, etc.).Suspension controller 820 may assume that the vehicle spring mass isonly supported by gas pressure. This assumption does not hold true whenthe spring is at a travel range limit (e.g., the spring is fullycompressed or fully extended). In such a case, suspension controller 820may adjust the spring away from the travel range limit to facilitatecalculating the mass. In some embodiments, the adjustment away from thetravel range limit is done without regard to a particular target springlength, since the mass estimation is calculable at any spring lengththat is not at a travel range limit. For example, the suspension may belowered until it is no longer hitting rebound stops or raised until itis no longer hitting jounce bumpers. One skilled in the art wouldappreciate that any calculations presented herein can be modifiedaccordingly to account for variations from these assumptions.

The suspension controller 820 may estimate the mass of the vehicle 800using measured pressure information from each of the spring assemblies,from data provided by a user, or from another source. Using theestimated mass of the vehicle 800, the suspension controller 820 maythen calculate P_(strut,target) for each of the spring assemblies. Thesuspension controller may perform a force and moment balance on thevehicle 800 in addition to applying other constraints on the targetpressures for each of the spring assemblies to solve forP_(strut,target). By way of example, in embodiments that include fourspring assemblies, the suspension controller 820 may require that aratio of the pressure in the front spring assembly to the pressure inthe rear spring assembly be equal on either side of the vehicle 800.This is intended to minimize cross-loading (e.g., where the front leftand rear right springs have a higher loading than the front right andrear left springs). By way of another example, in embodiments with tworear tractive assemblies 42, the suspension controller 820 may balancethe loading between the two rear tractive assemblies 42.

The present disclosure contemplates methods, systems, and programproducts on any machine-readable media for accomplishing variousoperations. The embodiments of the present disclosure may be implementedusing existing computer processors, or by a special purpose computerprocessor for an appropriate system, incorporated for this or anotherpurpose, or by a hardwired system. Embodiments within the scope of thepresent disclosure include program products comprising machine-readablemedia for carrying or having machine-executable instructions or datastructures stored thereon. Such machine-readable media can be anyavailable media that can be accessed by a general purpose or specialpurpose computer or other machine with a processor. By way of example,such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROMor other optical disk storage, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to carry or storedesired program code in the form of machine-executable instructions ordata structures and which can be accessed by a general purpose orspecial purpose computer or other machine with a processor. Wheninformation is transferred or provided over a network or anothercommunications connection (either hardwired, wireless, or a combinationof hardwired or wireless) to a machine, the machine properly views theconnection as a machine-readable medium. Thus, any such connection isproperly termed a machine-readable medium. Combinations of the above arealso included within the scope of machine-readable media.Machine-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing machines to perform a certain function orgroup of functions.

As utilized herein, the terms “approximately”, “about”, “substantially”,and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numerical ranges provided. Accordingly, these terms shouldbe interpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims.

It should be noted that the terms “exemplary” and “example” as usedherein to describe various embodiments is intended to indicate that suchembodiments are possible examples, representations, and/or illustrationsof possible embodiments (and such term is not intended to connote thatsuch embodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like, as used herein, mean thejoining of two members directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent, etc.) or moveable (e.g.,removable, releasable, etc.). Such joining may be achieved with the twomembers or the two members and any additional intermediate members beingintegrally formed as a single unitary body with one another or with thetwo members or the two members and any additional intermediate membersbeing attached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,”“above,” “below,” “between,” etc.) are merely used to describe theorientation of various elements in the figures. It should be noted thatthe orientation of various elements may differ according to otherexemplary embodiments, and that such variations are intended to beencompassed by the present disclosure.

Also, the term “or” is used in its inclusive sense (and not in itsexclusive sense) so that when used, for example, to connect a list ofelements, the term “or” means one, some, or all of the elements in thelist. Conjunctive language such as the phrase “at least one of X, Y, andZ,” unless specifically stated otherwise, is otherwise understood withthe context as used in general to convey that an item, term, etc. may beeither X, Y, Z, X and Y, X and Z, Y and Z, or X, Y, and Z (i.e., anycombination of X, Y, and Z). Thus, such conjunctive language is notgenerally intended to imply that certain embodiments require at leastone of X, at least one of Y, and at least one of Z to each be present,unless otherwise indicated.

It is important to note that the construction and arrangement of thesystems as shown in the exemplary embodiments is illustrative only.Although only a few embodiments of the present disclosure have beendescribed in detail, those skilled in the art who review this disclosurewill readily appreciate that many modifications are possible (e.g.,variations in sizes, dimensions, structures, shapes and proportions ofthe various elements, values of parameters, mounting arrangements, useof materials, colors, orientations, etc.) without materially departingfrom the novel teachings and advantages of the subject matter recited.For example, elements shown as integrally formed may be constructed ofmultiple parts or elements. It should be noted that the elements and/orassemblies of the components described herein may be constructed fromany of a wide variety of materials that provide sufficient strength ordurability, in any of a wide variety of colors, textures, andcombinations. Accordingly, all such modifications are intended to beincluded within the scope of the present inventions. Othersubstitutions, modifications, changes, and omissions may be made in thedesign, operating conditions, and arrangement of the preferred and otherexemplary embodiments without departing from scope of the presentdisclosure or from the spirit of the appended claim.

What is claimed is:
 1. A suspension system, comprising: a springassembly including: a gas spring; and an accumulator coupled to the gasspring and including a bladder, the accumulator having a compressedstate and an uncompressed state; and a controller configured to:determine a target amount of gas in the spring assembly; and adjust theamount of gas in the spring assembly towards the target amount of gasbased on a pressure difference across the bladder.
 2. The suspensionsystem of claim 1, further comprising at least one of: a first sensorarranged to detect a first pressure on a first side of the bladder; anda second sensor arranged to detect a second pressure on a second side ofthe bladder opposite the first side, wherein the controller isconfigured to determine the target amount of gas based on at least oneof the first pressure and the second pressure.
 3. The suspension systemof claim 2, wherein the accumulator includes a volume of gas locatedtherein, and wherein the controller is configured to determine thetarget amount of gas by multiplying the volume of gas in the accumulatorwith one of the first pressure and the second pressure.
 4. Thesuspension system of claim 3, wherein the controller is configured tomultiply the volume of gas in the accumulator with the greater of thefirst pressure and the second pressure.
 5. The suspension system ofclaim 4, wherein the first pressure is a preset pressure.
 6. Thesuspension system of claim 2, wherein the controller is configured todetermine the target amount of gas as a function of:P_(s,target)(V_(s,target)+V_(deadvol)) where P_(s,target) is a targetpressure for the gas spring, V_(s,target) is a target volume in the gasspring, and V_(deadvol) is a constant volume in the spring assembly. 7.The suspension system of claim 5, wherein the controller is configuredto: estimate a mass of a body acting on the gas spring; and calculatethe target pressure for the gas spring based on the estimated mass. 8.The suspension system of claim 1, wherein the controller is configuredto: determine a gas spring volume associated with a target springlength; determine a target pressure based on a mass of a body acting onthe gas spring; and determine the target amount of gas by 1) multiplyingthe target pressure and the gas spring volume and 2) adding thereto avolume of gas located in the accumulator multiplied by the greater of a)the target pressure and b) a pressure in the accumulator.
 9. Thesuspension system of claim 8, wherein the mass of the body is anestimated mass.
 10. A vehicle, comprising: a suspension system, thesuspension system including a spring assembly including: a gas spring;and an accumulator coupled to the gas spring and including a bladder,the accumulator having a compressed state and an uncompressed state; anda controller configured to: determine a target amount of gas in thespring assembly; and adjust the amount of gas in the spring assemblytowards the target amount of gas based on a pressure difference acrossthe bladder.
 11. The vehicle of claim 10, further comprising at leastone of: a first sensor arranged to detect a first pressure on a firstside of the bladder; and a second sensor arranged to detect a secondpressure on a second side of the bladder opposite the first side,wherein the controller is configured to determine the target amount ofgas based on at least one of the first pressure and the second pressure.12. The vehicle of claim 11, wherein the accumulator includes a volumeof gas located therein, and wherein the controller is configured todetermine the target amount of gas by multiplying the volume of gas inthe accumulator with one of the first pressure and the second pressure.13. The vehicle of claim 12, wherein the controller multiplies thevolume of gas in the accumulator with the greater of the first pressureand the second pressure.
 14. The vehicle of claim 11, wherein thecontroller is configured to determine the target amount of gas as afunction of:P_(s,target)(V_(s,target)+V_(deadvol)) where P_(s,target) is a targetpressure for the gas spring, V_(s,target) is a target volume in the gasspring based on a length of the gas spring, and V_(deadvol) is aconstant volume in the gas spring.
 15. The vehicle of claim 14, whereinthe controller is configured to: estimate a mass of a body acting on thegas spring; and calculate the target pressure for the gas spring basedon the estimated mass.
 16. The vehicle of claim 10, wherein thecontroller is configured to: determine a gas spring volume associatedwith a target spring length; determine a target pressure based on a massof a body acting on the gas spring; and determine the target amount ofgas by 1) multiplying the target pressure and the gas spring volume and2) adding thereto a volume of gas located in the accumulator multipliedby the greater of a) the target pressure and b) a pressure in theaccumulator.
 17. A method of controlling a gas spring in a suspensionsystem, the method comprising: detecting at least one of: a firstpressure on a first side of a bladder of an accumulator coupled to thegas spring; and a second pressure on a second side of the bladderopposite the first side; determining a target amount of gas in a springassembly that includes the accumulator and the gas spring; and adjustingthe amount of gas in the spring assembly towards the target amount ofgas based on a difference between the first pressure and the secondpressure.
 18. The method of claim 17, wherein the accumulator includes avolume of gas located therein, and wherein determining the target amountof gas comprises multiplying the volume of gas in the accumulator withthe greater of the first pressure and the second pressure.
 19. Themethod of claim 17, wherein determining the target amount of gascomprises determining the target amount of gas as a function of:P_(s,target)(V_(s,target)+V_(deadvol)) where P_(s,target) is a targetpressure for the gas spring, V_(s,target) is a target volume in the gasspring based on a length of the gas spring, and V_(deadvol) is aconstant volume in the gas spring.
 20. The method of claim 17, whereindetermining the target amount of gas comprises: determining a gas springvolume associated with a target spring length; determining a targetpressure based on a mass of a body acting on the gas spring; anddetermining the target amount of gas by 1) multiplying the targetpressure and the gas spring volume and 2) adding thereto a volume of gaslocated in the accumulator multiplied by the greater of a) the targetpressure and b) a pressure in the accumulator.